Look into the nursery of the universe

Astronomers discover a star system created shortly after the Big Bang

Galaxy BzK-15504 © Genzel et. al. / ESO
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An international team of astronomers has discovered large disk galaxies that resemble our Milky Way and must have formed in a relatively short time about three billion years after the Big Bang. Using the new SINFONI infrared spectrometer, the researchers at the European Southern Observatory's Very Large Telescope were able to study the anatomy of one of these galaxies with a record resolution of only 0.15 arcseconds. They were able to gather new knowledge about the formation of galaxies.

"For the first time, we have obtained such detailed images of the gas movement in a star system 11 billion light years away, " commented Reinhard Genzel, director at the Max Planck Institute for Extraterrestrial Physics in Garching in the current issue of the science journal Nature.

New theory of galaxy formation

Over the past decade, astronomers have developed a theory of galaxy formation and evolution in the young universe: gas from ordinary matter cooled and accumulated in concentrations of the mysterious dark matter. Afterwards, collisions and mergers of Milky Way systems led to the hierarchical structure of a galaxy. However, this fundamental scenario leaves open in which periods and when the galaxies have formed, and when and in what way their bulges and disks - the main components of today's star systems - have emerged.

Valuable answers have now been provided by the large-scale SINS study on far-off, bright young Milky Way galaxy systems called protogalaxies. The researchers at the Very Large Telescope used the innovative infrared spectrometer SINFONI, which in combination with a correction system produces sharp images and high-resolution color information of celestial objects.

In the case of the galaxy BzK-15504, which is about eleven billion light-years distant, the SINFONI observations achieved an angular resolution of 0.15 arcseconds. By comparison, the full moon appears in the earthly sky at an angle of 1, 800 arc seconds. This value corresponds to a distance of only 4, 000 light years in the distant star system. The pictures show a large, massive rotating proto-disk, which leads gas to a steadily growing core area with many young stars. display

High birth rates - low age

The researchers conclude that high birth rates and a comparatively low age of the stars. Therefore, they believe that this Milky Way system has formed rapidly - through fragmentation and star formation in a proto-disk that was originally very gas-rich. Observations on several other galaxies at high redshifts and thus large distances produced similar results.

"At the beginning of the program, we assumed that we could observe predominantly erratic and perhaps even chaotic movements, as they trigger the collisions of galaxies that occur frequently in the young Universe. We were all the more surprised when we discovered a series of large rotating and gas-rich disk galaxies, whose kinematic properties are very similar to those of today's Milky Way, "says Genzel.

Large and fast rotation of these galaxies are an indication that the gas has a comparable "spin" as the dark matter accumulations from which it has cooled off. In this way, an important question of galaxy formation can be answered empirically. Natascha F rster Schreiber, a Balzan scholarship holder at the Max Planck Institute in Garching, adds: "We must now try to understand how these early prototypes developed after that have not remained stable. "

The SINFONI data suggest that the protoplates eventually turned into dense elliptical disks - either through processes that took place inside them, such as spectacular gas flows as in the BzK-15504 object, or by collisions and mergers with other galaxies.

Galaxy formation becomes more transparent

Another important aspect, according to the researchers, are the very high star formation rates that could be derived for many of the high redshifted bright galaxies: there, the birth rate is about a hundred times higher than today in our Milky Way. "We have growing evidence that massive, distant galaxies have formed much faster than previously thought, " says Andrea Cimatti, team member and scientist at the University of Florence, "The new SINFONI data give us a first impression of which processes may be involved. "

The SINS program on the Very Large Telescope gives an idea of ​​what will become possible over the next few years with the combination of field-imaging spectrometer and adaptive optics. Alice Shapley, a researcher at the Princeton Observatory, explains, "These observations are really exciting, and now it's about getting similar excellent data for a larger number of galaxies to our knowledge." Continue to expand on galaxy formation. "

(MPG, 17.08.2006 - DLO)